These trolleys are tied to belts, chains or similar devices pulling them along rails comprising two essentially horizontal superimposed sections, connected by two curved sections on which the trolleys move from the upper to the lower path and vice versa.
A transport plane rigidly fastened to chains would in this process be flipped over, with the consequent dropping off of the transported items.
In order to prevent this, certain devices need to be supplied to constantly maintain the transport planes in an essentially horizontal position, even when they pass the curved sections connecting the upper horizontal plane with the lower plane of the path.
Switching machines of this type are already known, and one of these is for example described in the Italian patent application no. MI93A 0309 by the same applicant. This known switching machine comprises several trolleys, each of which fitted with a rotating mat which constitutes the item's transporting and unloading plane.
The trolleys are hinged to a pair of chains pulled in a rotating motion along a vertical plane by sprockets. At the connecting points between the upper and the lower path, certain devices are supplied which keep the trolleys in a horizontal position while passing from one section of the path to another, thus preventing them from flipping over.
In particular, these devices consist of tongs mounted on discs coaxial with the chains' pulling wheels and moving in a synchronized fashion with the latter, engaging the mentioned trolleys so as to keep them in an essentially horizontal position while passing from an upper to a lower section of the course, and vice versa.